Rotary hearth furnaces for the heating of particulate material in controlled atmospheres are well known and are described in Kemmerer, et al. U.S. Pat. No. 3,470,078 of Sept. 30, 1969 and Oleszko, U.S. Pat. No. 3,652,426 of Mar. 28, 1972. A stationary hearth rotary roof furnace for that purpose is disclosed in Johnson, et al. U.S. Pat. No. 4,669,977 of June 2, 1987. A disadvantage of both types of furnace where the atmosphere must be controlled is the seal between the hearth and furnace chamber or between the roof and furnace chamber. Hearth diameters of 25 feet are not uncommon and the extent of the seal required for such furnaces limits the sealing material to a granular substance such as sand or to a liquid, generally water. A liquid seal can be made quite effective; however, water reacts with some of the gases evolved when coal is heated under controlled conditions. The rotary hearth of our invention is totally enclosed and sealed.